18 Wenham_, on a Binocular and Single Microscope, 
lopment^ we hover at length in pleasing uncertainty at the 
confines where the plant may be supposed to end and animal 
life commence. The waistcoat- pocket may conceal our 
menagerie,, and any locality furnish objects. For example, 
at this season of the year, draw from the nearest hedge-side 
ditch a rotten leaf. " Drop it again/^ the unknowing would 
say in disgust, it is decomposing, and covered with a loath- 
some-looking slime ; but remove a portion of this, and place 
it under the microscope, and marvellous is the living host 
displayed to view, consisting of Diatomacece, Desmidice, OsciU 
latoria, Ammbce, Rotifers, &c., all assembled together in 
one dense crowd, perfect in beauty and cleanliness. An hour 
may pass away unheeded, in the interest caused by observing 
the movements of these creatures ; but greatly is that interest 
enhanced by the aid of binocular vision ; they appear then 
not as mere moving discs, but in all the reality due to life and 
substance. 
The chief inconvenience of all the binocular microscopes 
hitherto made, besides distorted or imperfect definition, has 
.been the necessity of a separate double body ; and the con- 
stant trouble of shifting this for the single tube very much 
limits their utility. There is also the difficulty of cleaning 
the prisms, and a liability to their derangement. In the in- 
strument I have now to describe these objections do not 
exist ; for the eff'ect, as a single microscope, is not in the 
slightest degree impeded or interfered with, and by a touch 
of the finger it is instantly converted into a binocular, or 
back again. The annexed diagram will explain the principle 
of action ; a is the body of an ordinary microscope, moved 
perpendicularly relative to the stage, with fine motion, &c., 
precisely as it is commonly made. On the right-hand side, 
in the neck at b, is cut a square hole, through which a prism, 
c, having two reflecting surfaces, is made to slide, as close 
behind the object-glass as possible. This prism is held by 
the ends only in the sides of a small drawer, so that all the 
four polished surfaces are accessible, and should slide in so 
far that its edge may just reach the central line of the ob- 
jective, and be drawn back against a stop, so as to clear the 
aperture of the same altogether, in which case the tube a acts 
without impediment as a single microscope. When the 
prism is thrust in more or less, it collects a portion of the 
rays and reflects them to the opposite side of the tube, at 
D, where an opening is to be made large enough to admit 
them all, under extreme conditions. Parallel with the direc- 
tion of these rays is grafted on " the supplementary tube 
with eye-pieces, &c., and in size corresponding with the 
